A manipulator normally has a main-support arm that is carried on a link and that can be moved about parallel horizontal axes at each end of the link. In addition the link is mounted on a base which can pivot about a vertical axis.
The free end of the main support arm carries a small housing which can be rotated about the longitudinal axis of the arm and which in turn carries a so-called head which can be pivoted on the housing about a transverse axis perpendicular to the main longitudinal axis of the support arm. Finally a small tool or workpiece holder is mounted on the head and is itself rotatable thereon about the longitudinal axis of the head, which can be set by pivoting of the holder about the transverse axis to be parallel to or at an angle to the main support axis. A tool such as a spot welder carried by the tool holder can therefore be set at virtually any angle to a workpiece by such a manipulator.
Such a drive, as described in German patent publication No. 2,619,336, is relatively bulky. Each of the three degrees of motion is powered by a respective electric or hydraulic drive motor connected to the housing through concentric tube shafts. Since the head and holder must be able to pivot about the transverse axis, it is necessary to provide right-angle drives for these parts, to transmit the necessary drive torque through the joint. Normally such drives incorporate at least one shaft parallel to the transverse axis, on the main support, and connected to at least one other shaft at the transverse axis. In fact such a manipulator is normally so bulky that mounting tools on it is difficult. The head is largely recessed in the housing, making the head portion relatively massive and hard to fit into tight locations.
As it is normally desirable to use high-speed low-torque motors for such a drive, it is necessary to provide stepdown transmissions. Typically, as in the above-cited patent document, such transmissions are provided right on the motors. Such an arrangement requires virtually no losses or backlash in the gearing between the transmissions and the controlled elements, as any such losses or play would be synergistically cumulative at the controlled element to make it impossible to position the controlled element exactly.
Another such manipulator drive is known from German patent publication No. 2,402,829. Here the head is largely recessed in the housing and between the relatively narrow head and the side wall of the housing there are two parallel longitudinal intermediate shafts. These shafts are connected via bevel gears to the output for the head and support. In this arrangement also the stepdown transmissions are provided well upstream so that these shafts rotate slowly and rarely through much more than 360.degree..
Normally most of this mechanism is provided out on the support arm or housing. As a result the moment resulting from this large mass at the end of this relatively long lever is quite great. Thus the manipulator is relatively unwieldy, and requires heavy-duty motors to move itself.